pH Sensing

The basic pH sensor consists of two bundled optical fibers facing a reflector. A dye is stuck onto the reflector. The input fibers couple light from the opto-electronic unit into the gap between the fiber tips and the reflector. Light propagates through the dye, is reflected and then re-coupled into the output fibers. The opto-electronic unit measures the amount of reflected light. The optical absorption of the dye depends on the pH of the solution surrounding the probe. Thus, the ratio between the emitted optical power and the detected optical power provides a measure of the pH value. An additional reference channel consisting of another pair of fibers in connection with an uncoated reflector provides the possibility of drift compensation.